1. Field of the Invention
The invention relates to a method for machining a workpiece by means of laser radiation injected and guided in a liquid jet, in which the liquid jet having the laser radiation is directed on to a surface of the workpiece and the workpiece is machined at an operating point. The invention relates, further, to a device for machining a workpiece by means of laser radiation which can be directed on to a surface of the workpiece, the workpiece being capable of being machined at an operating point, and the laser radiation being injected and guided in a liquid jet.
2. Description of the Related Art
Laser radiation can be used, particularly in industry, in many different ways for machining the most diverse possible materials, such as, for example, metals, plastics or even ceramics. Machining ranges from cutting, drilling and welding through to material removal or marking.
Typically, in the machining of a workpiece by laser radiation, material is removed from the workpiece. In this case, small material particles occur, what are known as ejections, which settle or melt on the surface of the workpiece again. Depending on the nature of the workpiece and/or of the workpiece surface or of the ejections, it may happen that these bond firmly with one another again. These deposits on the surface of the workpiece may adversely influence the properties of the final product and are therefore usually undesirable. If at all possible, therefore, they have subsequently to be removed again at high outlay. Further, during machining by laser radiation, the workpiece is typically heated, and this may likewise entail undesirable consequences for the workpiece.
WO/9532834 discloses a device in which the laser radiation is injected into a liquid jet which acts as a light guide. As a result, not only can the energy of the laser radiation be brought to the operating point, but the liquid at the same time acts as a coolant which efficiently cools the workpiece in the machining region. Furthermore, vapors, particles and aerosols which occur during machining by laser radiation can be bound or prevented. However, the liquid quantity of the liquid jet into which the laser radiation is injected is not sufficient to flush away completely the ejections occurring during machining.
U.S. Pat. No. 3,991,296 A discloses a further device for machining and segmenting a wafer by means of a laser. In order to prevent machining residues from sticking to the wafer, a closed interspace, through which deionized water flows, is produced, just above the wafer, with the aid of a transparent glass plate. The laser beam directed on to the wafer penetrates through the glass plate and the water layer and then cuts the wafer, while the water is intended to cool the residues occurring in this case and thus to prevent the residues from sticking to the wafer. After cutting, these residues are then simply to be washed away, at most with the aid of low ultrasound.
The disadvantages of this device are that the water layer on the wafer disturbs the laser radiation in such a way (refraction, diffusion, damping) that the laser beam loses both sharpness and energy, so that the workpiece cannot or can no longer be machined efficiently. Moreover, in the method described, it is difficult or even impossible to discharge the melt occurring during machining out of the machining region, since the glass plate prevents the use of a cutting gas. Finally, in spite of the water layer, subsequent cleaning of the final product is necessary.
US 2003/129 814 A1 describes a further method for machining a semiconductor element by means of a laser beam. In order to avoid the diffusion of the laser light on the residues, the silicon substrate is tilted to one side and flushed over with water. As a result, the residues are flushed away around the operating point, and cooling of the substrate takes place at the same time.
In this method, too, the laser beam is diffused and damped by the water layer, thus making it difficult or even impossible to carry out the machining of the silicon substrate. Further, here too it is not possible to discharge the melt out of the machining region on the silicon substrate, since cutting gas which expels the melt cannot be used.